1. Field of the Invention
This invention relates generally to electromagnetic interference shields, and more particularly to textile electromagnetic interference shields.
2. Related Art
It is known to fabricate electromagnetic interference (EMI) shields 1 entirely from wire, such as shown in FIG. 1. The wire, being too stiff to be knit, is generally woven to form a mesh of a predetermined mesh size to prevent the passage of EMI therethrough, thereby acting as a barrier or shield to the EMI.
The manufacture of woven wire EMI shields is not a simple process. The metal wire material typically employed in such woven EMI shields is fairly stiff and this lends to the material being generally difficult to weave. Special care must be taken in controlling the process to ensure that a uniform mesh size is achieved and this adds to the cost and complexity of producing such a product. And it is important to control the mesh size to produce an EMI shield with uniform properties and to make certain that the mesh size is not so large as to permit the transmission of EMI through the shield. Careful controls must be in place to obtain a commercially usable product.
A further disadvantage of woven wire EMI shields, apart from the difficulty in manufacturing them, is their robustness when placed in service. When first installed, the mesh size is desirably present in its as-manufactured uniform condition and would be effective at shielding EMI. However, it has been found that the woven nature of such shields enables the relative positions of the wires to shift either during installation or over time, with some of the wires getting pushed closer together while others end up being drawn further apart. Such change in the mesh size is undesirable as it yields inconsistent performance from one product to another and even within the mesh field of a given product. Moreover, in cases where the wires have shifted apart to increase the mesh size (either locally or over a larger region or regions), the increased gap can be large enough to allow EMI to pass through the shield which is highly undesirable.